biquad.h

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#ifndef BIQUAD_H
#define BIQUAD_H
 
#include <math.h>
#include <stdlib.h>
 
#ifndef M_LN2
#define M_LN2 0.69314718055994530942
#endif
 
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
 
/* The sample type used throughout.  Change to float if you want
 * single-precision processing (saves memory, slightly less accurate). */
typedef double smp_type;
 
typedef struct {
    smp_type a0, a1, a2, a3, a4;  /* filter coefficients   */
    smp_type x1, x2;              /* input delay line       */
    smp_type y1, y2;              /* output delay line      */
} biquad;
 
smp_type BiQuad(smp_type sample, biquad *b);
 
biquad *BiQuad_new(int type, smp_type dbGain,
                   smp_type freq, smp_type srate,
                   smp_type bandwidth);
 
enum FILT_TYPE {
    LPF,   /* Low-pass filter   */
    HPF,   /* High-pass filter  */
    BPF,   /* Band-pass filter  */
    NOTCH, /* Notch filter      */
    PEQ,   /* Peaking band EQ   */
    LSH,   /* Low shelf filter  */
    HSH    /* High shelf filter */
};
 
#endif /* BIQUAD_H */